Alternating azimuth sweep



l atented July 31, 1951 ALTERNATING AZIMUTH SWEEP Merle A. Starr, Belmont, Mass, assignor, "by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application October 30, 1945; Serial No. 625,667

This invention relates to electric sweep circuits and more particularly to an alternating sweep for presenting azimuth information on a B-scan indicator of a radar system.

For the usual radar system B-scan presentation on a cathode ray tube, hereinafter referred to as CRT, the azimuth sweep of the CRT follows the orientation of the antenna in its scanning operation.

The present invention applies particularly to a two reflector antenna system where the azimuth angle between the reflectors is varied continuously so that their beams are swept first apart and then together in azimuth scanning. Using a CRT as the indicating means, the CRT beam must jump from side to side horizontally on the screen and the magnitude of the beams excursions from the center of the screen must be correlated with the angle between the reflectors. This is accomplished by applying to the horizontal deflection coils of the CRT periodic square waves which are 180 out of phase and-whose amplitudes correspond to the angle between the reflectors and are controlled by potentiometers linked to the reflectors. Range information is plotted vertically as usual on the B-scan.

An object of this invention is to provide a sweep circuit for generating phase opposed periodic square waves which are amplitude modulated in a predetermined manner.

Another object is toprovide a method of presenting information on a B-scan concerning the azimuth angle between two reflectors and the azimuth sweep of their radar beams.

Another object is to provide apparatus for indicating visually the azimuth sector being scanned by a two reflector antenna system.

These and other objects and features of this invention will become apparent upon consideration of the following detailed description when taken together with the accompanying drawing, which illustrates a typical embodiment of this invention. p

The figure illustrates the sweep circuit producing amplitude modulated square waves applied to the azimuth deflection coils of the cathode ray tube. The dotted lines to the reflectors indicate that the potentiometer arms are driven by mechanical linkage to the reflectors.

In the flgure, an alternating current sinusoidal wave I is applied to primary winding 2 of transformer 3. The secondary 4 of transformer 3 is center-tapped to ground at 5 so that the voltages 6 and 1 at either end of the secondary winding 4 are 180 out of phase. The voltages 6 and 1 are 5 Claims. (01. 343-113) through resistor land the plates receive 3+ through resistors l4 and 15 respectively. Tubes 8 and 9. are overdriven so that their plate output wave forms II and I2 are substantially squared waves. Qutput Wave II is out of phase with wave [2 but both are of the same frequency as wave I. 'Wa've II is applied through capacitor [6 to the control grid of tube 20 which is grounded through resistor I8. Wave [2 is applied through capacitor [1 to the control grid oftube 2! which is grounded through resistor is. The cathodes of tubes 20 and 2t are connected together and to one end of capacitor 24 whose other end is,

grounded. The cathodes are also connected to slider arm 27 and are biased by voltage tapped oil by slider arm 21 of potentiometer 25, one end of which is tied at 26 to a source of negative voltage and the other end of which connects to" one end of potentiometer 28. The other end of potentiometer 28 connects to a source of positive potential at point 29 and its slider arm 30 supplies positive potential through resistor 33 to the plate oftube 20 and through resistor 34 to the plate of tube 2|. Sliders 21 and 30 are driven by mechanical linkage by reflectors 35 and 36 on the antenna so that when the reflectors sweep out from the center, sliders 21.

and 3|! sweep towards the right as indicated y the arrows on the figure.

The plates of tubes 20 and 2| are also tied to.

the control grids of tubes 31 and 38 respectively, between whose cathodes is connected potentiometer 39, having a slider arm 40 which is grounded. B+ is supplied to the plate of tube 37. through the CRT azimuth deflection coil 4| and to the plate of tube 38, through the second azimuth deflection coil 42. The periodic current wave forms 43 and M are the plate outputs of tubes 37 and 38 appearing in deflection coils il and 42 respectively and have the frequency of thesinusoidal input wave I.

In one method of operation of the two reflectorscanner system, the radar beam is transmitted alternately from the reflectors and from only; one reflector at a time; The sinusoidal wave I has the frequency of the switching of the beam from one reflector to the other. This Wave is passed through transformer 3 and through the overdriven tubes 8 and 9 and the resulting squared waves II and I2 are applied to the control grids of tubes 20 and 2|. The control grids of tubes 31 and 38 are held at a positive potential determined by the circuit back to point 29, 

